[Xperia Z5 General] Phazonclash:
That pretty much sums up what I've experienced too with my Z5 so far.

At first I was super happy: The phone is very well built and it feels very premium/solid when you hold it. I'm a fan of the Sony design and I think it's the best looking phone on the market right now (with the Moto X Pure). The Xperia UI doesn't look half-bad, it even looks better than the stock Android UI in my opinion. The camera snaps pretty solid pictures and the 1080p60 video mode is pure gold. The loudspeakers are impressive, the screen looks great and the IP67 rating is just awesome

But after a few weeks many issues and annoyances appeared and made me realize that the Z5 is far from being stellar or far from being a phone I would recommend...

The firmware in general feels very rough around the edges and unfinished once you start digging deeper and using more advanced functionalities/features:

-Wifi thetering has been broken since October for me, and it's annoying as hell because I used that feature a lot with my Surface Pro

-Bluetooth connectivity is very unstable and unreliable in my car. I can't blame my car, I've never had problems before with my OnePlus One and Note 3. Since I have the Z5, it disconnects a lot, sometimes refuse to connect and it requires a reboot, etc.

-Auto-brightness seems broken or works eratically.

-I notice UI lag here and there, and it shouldn't happen on a Snapdragon 810 device. My old OnePlus One (Snapdragon 801) felt snappier and CM12.1 was buttery smooth. I can't say the same about Sony's UI.

-Maybe once a a day, an app (always a different app) will freeze and require a Force Close. Once I force closed it, I won't be able to launch it again without rebooting the phone.

-When there's 7 or more notifications from the same app on the lock screen, instead of showing all the notifications when you expand, you will only see a "@" followed by a chain of character. That's a known bug that has been patched months ago on CyanogenMod, and it's always present on Sony's ROM after many updates. That's annoying, it feels "unfinished" and unrefined. It makes it feel like the Z5 is running a beta firmware. That left me a bad impression when I first saw that bug again, on the Z5... it has been patched for months on my OnePlus One.

-So far, battery life has been subpar and acceptable at best. I know about the Lollipop "mobile radio active" bug and all, but still... I expected a little bit more.

-Sometimes, for no apparent reason, the phone will become very sluggish, with many little "delays" here and there to execute some simple tasks (open an app, open the Notifications Center, etc.) That's something I've never experienced before with my older (and slower on paper) phones. I think the firmware is the culprit

That's what came to my mind, but there's more issues and inconsistencies.

You know, I've had a OnePlus One from day 1 (well almost) and I went through all the early firmware problems they had. I'm not the most exigent and demanding user, but I like to see some progress and bugfixes... I knew OnePlus was a new company and I knew the One were their first phone... with time, the ROM got better and better, and a year layer when I sold it, the One was a pretty solid and enjoyable device.

But the thing is... Sony isn't OnePlus... they've been selling phones for a while now and I expected a lot more. I didn't expect the impossible, but I think it was fair to expect a phone that wouldn't have bluetooth issues, auto-brightness that works, a lag free UI experience, etc.

Sadly, that's not what I got... The current Lollipop firmware feels very "beta-ish" to me... it feels like a firmware that would ship with a Chinese 150$ phone!

Now all I hope is that Marshmallow will be better. In the current state, and if these issues are still present in Marshmallow, I will get rid of that phone and get a Nexus.

As a matter of fact, I've been using my old Galaxy Note 3 + CM13 for the last 6 weeks now... It doesn't crash, bluetooth just works, I can go through the day easily on a single charge and, in general, I enjoy using it more than my Z5 despite the fact that it's an old phone by today's standards... I still prefer an older phone that just works, than a newer phone that has the issues I described earlier.

The Z5 is my first Sony phone and probably my last to be honest. They failed to leave me with a good impression... For those who use older models like the Z3 or Z3+: the Sony firmware was that buggy when you got your phone? Did it get better with time and updates?